Process for preparing a stabilized polyester

ABSTRACT

The present invention discloses a process for the preparation of a stabilized polyester that is low in the generation of aldehydes which comprises reacting one or more diacids with one or more diols in an esterification process, and/or one or more diesters with one or more diols in a transesterification process in the presence of an effective amount of a stabilizer selected from the group consisting of (a) a polyhydric alcohol which is for example poly(ethylene-co-vinyl alcohol), poly(styrene-co-allyl alcohol), maltitol, isomalt, sorbitol, xylitol, sucrose, mucic acid dibutylester, mucic acid di(phenyl-1-ethyl)ester, pentaerythritol or dipentaerythritol; (b) a compound of the formula II, which is for example di-iso-octyl-phosphinic acid; (c) a sterically hindered amine which is for example Tinuvin 123 or Tinuvin 622; (d) a polyacrylamide or a cationic acrylamide copolymer, or (e) a hydroxyamine and/or a nitrone. Such polyesters, for example PET, when extrusion compounded exhibit a lower residual acetaldehyde content than does PET alone when similarly treated. The invention pertains to any polyester used in the manufacture of bottles or containers which in turn are used to store consumer materials, especially food, pharmaceuticals, beverages and most especially water.

[0001] The present invention discloses a process for the preparation ofa stabilized polyester that is low in the generation of aldehydes whichcomprises reacting one or more diacids with one or more diols in anesterification process, and/or one or more diesters with one or morediols in a transesterification process in the presence of an effectiveamount of a stabilizer selected from the group consisting of (a) apolyhydric alcohol; (b) a phosphinic acid; (c) a sterically hinderedamine; or (d) a polyacrylamide. Such polyesters, for example PET, whenextrusion compounded exhibit a lower residual acetaldehyde content thandoes PET alone when similarly treated. The invention pertains to anypolyester used in the manufacture of bottles or containers which in turnare used to store consumer materials, especially food, pharmaceuticals,beverages and most especially water.

[0002] A low amount of contaminants (e.g. aldehydes) in polyester waterbottles is beneficial for improved taste or flavor in bottled water orother bottled beverages in said containers. The reduction in the amountof acetaldehyde in polyethylene terephthalate (PET) is highly beneficialin this respect. Acetaldehyde is known as a decomposition product ofpolyesters such as PET. The acetaldehyde imparts an undesirable taste orflavor to bottled water stored in polyethylene terephthalate bottles. Ithas been a long sought objective of the industry to reduce the level ofacetaldehyde which migrates out of the PET bottle walls into the wateror other beverage stored therein. A number of engineering or designchanges to extruders, injection molding machines for preforms and bottlemaking machinery have been made to minimize formation of acetaldehydewhen PET is processed. Modification to the PET composition itself havebeen made to lower its melting point or its melt viscosity in order toallow less severe thermal or mechanical damage when PET is processedinto preforms or bottles.

[0003] U.S. Pat. No. 5,235,027 teaches the preparation of a modifiedcopolyethylene terephthalate for processing by extrusion blow moldingwith a low acetaldehyde content in the presence of a tri- ortetrahydroxyalkane.

[0004] WO-A-00/73379 discloses a process for preparing a stabilizedpolyester that is low in the generation of aldehydes by reacting one ormore diacids with one or more diols in an esterification process, and/orone or more diesters with one or more diols in a transesterificationprocess, and adding a phosphorus-containing stabilizer to a polyesterbetween the end of the melt phase and prior to subsequent secondarymelting of the polyester in processing to the final article such as abottle, characterized in that the stabilizer comprises one or moretri(phenyl) phosphites, wherein each phenyl group independently containsat least one substituted ortho position and, optionally mixed with oneor more phenolic antioxidants.

[0005] These known processes for preparing polyesters do not satisfy inevery respect the high requirements which a polyester is required tomeet, especially with regard to aldehyde content of the polyester afterextrusion to an end-use article like a bottle for mineral water, colorproperties and transparency. As a result there continues to be a needfor an improved process for the preparation of polyesters.

[0006] The instant invention pertains therefore to a a process for thepreparation of a stabilized polyester that is low in the generation ofaldehydes which comprises reacting one or more diacids with one or morediols in an esterification process, and/or one or more diesters with oneor more diols in a transesterification process in the presence of aneffective amount of a stabilizer selected from the group consisting of

[0007] a) a polyhydric alcohol of the formula I

E—(OH)_(n)  (I)

[0008]  wherein n is 3 to 4000, and

[0009]  E is an aliphatic, cycloaliphatic, aromatic or a mono-, di- orpoly-sucrose moiety; with the proviso that, if n is 3 or 4 and E is analiphatic moiety, then additionally at least one sterically hinderedhydroxyphenylalkylphosphonic ester or monoester is present;

[0010] b) a compound of the formula II

[0011]  wherein

[0012]  R₁ is hydrogen, C₁-C₂₀alkyl, phenyl or C₁-C₄alkyl substitutedphenyl; biphenyl, naphthyl, —CH₂—O—C₁-C₂₀alkyl or —CH₂S—C₁-C₂₀alkyl,

[0013]  R₂ is C₁-C₂₀alkyl, phenyl or C₁-C₄alkyl substituted phenyl;biphenyl, naphthyl, —CH₂—O—C₁-C₂₀alkyl or —CH₂—S—C₁-C₂₀alkyl, or R₁ andR₂ together are a radical of the formula III

[0014]  wherein

[0015]  R₃, R₄ and R₅ independently of each other are C₁-C₂₀alkyl,phenyl or C₁-C₄alkyl substituted phenyl,

[0016] c) a sterically hindered amine which comprises at least a radicalof the formula IV or V

[0017]  wherein

[0018]  G is hydrogen or methyl, and

[0019]  G₁ and G₂ are hydrogen, methyl or together are oxygen,

[0020] d) a polyacrylamide of the formula VI

[0021]  wherein

[0022]  R′₁, and R′₂ are independently of each other hydrogen,C₁-C₂₀alkyl, phenyl or C₁-C₄-alkyl substituted phenyl; biphenyl,naphthyl, —CH₂—O—C₁-C₂₀alkyl or —CH₂—S—C₁-C₂₀alkyl; or R′₁ and R′₂together are a radical of the formula III

[0023]  R′₁ and R′₂ together with the nitrogen atom to which they areattached form an unsubstituted or C₁-C₄alkyl substituted imidazolyl,pyrrolyl, pyrrolidonyl, piperidinyl or piperazinyl ring; and

[0024]  q is 5 to 300000; or

[0025]  a polyacrylamide copolymer wherein the comonomer is an acrylicacid, an acrylic acid salt or an acrylic ester; or

[0026] e) hydroxylamines and/or nitrones.

[0027] Of interest is a process comprising components (a), (b), (c) or(d) with the proviso that the comonomer in component (d) is acrylic acidor an acrylic ester.

[0028] Also of interest is a process comprising in addition tocomponents (a), (b), (c), (d) or (e) at least one sterically hinderedhydroxyphenylalkylphosphonic ester or monoester [component (f)].

[0029] Of special interest is a process comprising all components (a),(b), (c), (d), (e) and (f) in any combination, for example (a) (b); (a)(c); (a) (d); (a) (e); (a) (f); (b) (c); (b) (d); (b) (e); (b) (f); (c)(d); (c) (e); (c) (f); (d) (e); (d) (f); (a) (b) (c); (a) (b) (d); (a)(b) (e); (a) (b) (f); (b) (c) (d); (b) (c) (e); (b) (c) (f); (c) (d)(e); (c) (d) (f); (a) (d) (e); (b) (d) (e); (c) (d) (e); (a) (c) (d);(a) (c) (e); (a) (b) (c) (d); (a) (b) (c) (e); (b) (c) (d) (e); (a) (c)(d) (e) or (a) (b) (c) (d) (e).

[0030] Components (a), (b), (c), (d) or (e) and optionally thesterericlly hindered hydroxyphenylalkylphosphonic ester or monoester areused for example in an amount of 0.005 to 1% by total weight of thereactants, preferably in an amount of 0.01 to 0.30% by total weight ofthe reactants.

[0031] A preferred sterically hindered hydroxyphenylalkylphosphonicester or monoester is a compound of the formula VII

[0032]  wherein

[0033]  R₆ is isopropyl, tert-butyl, cyclohexyl or cyclohexyl which issubstituted by 1-3 C₁-C₄alkyl groups,

[0034]  R₇ is hydrogen, C₁-C₄alkyl, cyclohexyl or cyclohexyl which issubstituted by 1-3 C₁-C₄alkyl groups,

[0035]  R₈ is C₁-C₂₀alkyl, unsubstituted or C₁-C₄alkyl-substitutedphenyl or naphthyl,

[0036]  R₉ is hydrogen, C₁-C₂₀alkyl, unsubstituted orC₁-C₄alkyl-substituted phenyl or naphthyl; or is $\frac{M^{r +}}{r};$

[0037]  M^(r+) is an r-valent metal cation,

[0038]  p is 1, 2, 3, 4, 5 or 6, and

[0039]  r is 1, 2 or 3.

[0040] C₁-C₂₀alkyl substituents are radicals such as methyl, ethyl,propyl, butyl, pentyl, hexyl, octyl, stearyl or corresponding branchedisomers; C₂-C₄alkyl radicals are preferred.

[0041] C₁-C₄alkyl substituted phenyl or naphthyl, which preferablycontains 1 to 3, in particular 1 or 2, alkyl groups, is, for example,o-, m- or p-methylphenyl, 2,3-dimethylphenyl, 2,4-dimethylphenyl,2,5-dimethylphenyl, 2,6-dimethylphenyl, 3,4-dimethylphenyl,3,5-dimethylphenyl, 2-methyl-6-ethylphenyl, 4-tert-butylphenyl,2-ethylphenyl, 2,6-diethylphenyl, 1-methylnaphthyl, 2-methylnaphthyl,4-methylnaphthyl, 1,6-dimethylnaphthyl or 4-tert-butylnaphthyl.

[0042] C₁-C₄alkyl substituted cyclohexyl, which preferably contains 1 to3, in particular 1 or 2, branched or unbranched alkyl radicals, is, forexample, methylcyclohexyl, dimethylcyclohexyl, trimethylcyclohexyl ortert-butylcyclohexyl.

[0043] A monovalent, divalent or trivalent metal cation is preferably analkali metal cation, alkaline earth metal cation, heavy metal cation oraluminium cation, for example Na⁺, K⁺, Mg⁺⁺, Ca⁺⁺, Ba⁺⁺, Zn⁺⁺ or Al⁺⁺⁺.Particular preference is given to Ca^(++.)

[0044] Preferred compounds of the formula VII are those which contain atleast one tert-butyl group as R₆ or R₇. Very particular preference isgiven to compounds of the formula VII in which R₆ and R₇ aresimultaneously tert-butyl.

[0045] p is preferably 1 or 2, very particularly preferably 1.

[0046] Very particularly preferred sterically hinderedhydroxyphenylalkylphosphonic ester or monoester are the compounds of theformula P1 and P2.

[0047] The compound of the formula P1 is commercially available asIrganox 1425 (RTM) and that of the formula P2 is commercially availableas Irganox 1222 (RTM) both from Ciba Specialty Chemicals Inc..

[0048] Preferred diacids are selected from the group consisting ofaromatic dicarboxylic acids having 8 to 14 carbon atoms, aliphaticdicarboxylic acids having 4 to 12 carbon atoms, cycloaliphaticdicarboxylic acids having 8 to 12 carbon atoms, and mixtures thereof.

[0049] Preferably such diacids are terephthalic acid, isophthalic acid,o-phthalic acid, naphthalene dicarboxylic acid, cyclohexane dicarboxylicacid, cyclohexanediacetic acid, diphenyl-4,4′-dicarboxylic acid,succinic acid, glutaric acid, adipic acid, sebacic acid and mixturesthereof.

[0050] Especially preferred are terephthalic acid and 2,6-naphthalenedicarboxylic acid.

[0051] Preferred diols are compounds of the formula VIII

HO—R—OH  (VIII)

[0052] wherein R is an aliphatic, cycloaliphatic or aromatic moiety of 2to 18 carbon atoms.

[0053] Preferably such diols are for example ethylene glycol, diethyleneglycol, triethylene glycol, propane-1,3-diol, propane-1,2-diol,butane-1,4-diol, pentane-1,5-diol, hexane-1,6-diol,1,4-cyclohexanedimethanol, 3-methylpentane-2,4-diol,2-methylpentane-1,4-diol, 2,2-diethylpropane-1,3-diol,1,4-di-(hydroxyethoxy)benzene, 2,2-bis(4-hydroxycyclohexyl)-propane,2,4-dihydroxy-1,1,3,3-tetramethylcyclobutane,2,2-bis-(3-hydroxyethoxyphenyl)propane,2,2-bis-(4-hydroxypropoxyphenyl)ethane and mixtures thereof.

[0054] Most preferably, the diol is ethylene glycol or1,4-cyclohexanedimethanol.

[0055] Instead of, or in addition to the diacids mentioned above,various diesters may be used. For example, diesters that correspond inrespect of their acid moiety to the aforementioned diacids may be used.Suitable diesters therefore also include the aliphatic and the aromatickind. Very suitable diesters are for example the C₁-C₄alkyl esters ofterephthalic acid, isophthalic acid, o-phthalic acid or naphthalenedicarboxylic acid.

[0056] Preferably, the esterification and transesterification processesare carried out in the presence of a catalyst.

[0057] Catalysts of interest for the esterification process are forexample antimony or germanium compounds, e.g. antimony(III)oxide (Sb₂O₃)or germanium dioxide (GeO₂). Of interest are also titanium catalysts asdisclosed for example in DE-A-19 513 056 or titanium based catalysts incombination with cobalt and phosphorous based compounds as disclosed forexample in DE-A-19 518 943.

[0058] Catalysts of interest for the transesterification process are forexample titanium compounds, e.g. titanium(IV)butoxide.

[0059] The catalysts are preferably used in the preparation ofpolyesters in an amount of 0.005 to 0.035% by weight of the total amountof reactants.

[0060] Polyesters may be produced in a conventional batch process,wherein the product of the transesterification or sterification isformed in one vessel and then transferred to a second vessel forpolymerization. The second vessel is agitated and the polymerizationreaction is continued until the power used by the agitator reaches alevel indicating that the polyester melt has achieved the desiredintrinsic viscosity and therefore, the desired molecular weight. Forexample, in the preparation of polyethylene terephthalate (PET), theesterification or transesterification is typically conducted at anelevated temperature between for example 200 to 350° C. to produce apolyester having an intrinsic viscosity of 0.3 to 0.8 dl/g, commonlyabout 0.6 to 0.75 dl/g (determined by ASTM D-4603-86 at 30° C. in amixture of 60% by weight of phenol and 40% by weight oftetrachloroethane).

[0061] Alternatively, these steps may also be carried out in acontinuous process. For example, the continuous process disclosed inWO-A-97/44376 is conducted by combining the diol with the diacid ordiester at a temperature of about 240 to 290° C. and at a pressure offrom about 30 to 600 kPa for about 1 to 5 hours to yield low molecularweight oligomers and water. In general, a continuous feed of reactantsis used employing a molar ratio of diol to diacid or diester of fromabout 1.0 to 1.6. The water or alcohol so produced is removed as thereaction proceeds.

[0062] In the second stage of the continuous process, which is apolycondensation stage generally conducted in a series of 2 or morevessels, the oligomers are agitated at a temperature of about 240 to305° C. for about 1 to 4 hours in the presence of a polymerizationcatalyst to form the polyester melt.

[0063] Typically, the polycondensation reaction begins in a first vesseloperated at a pressure range of from about 0 to 10 kPa. Diol produced inthe polycondensation is removed from the polyester melt using an appliedvacuum. The polyester melt is typically agitated to allow the diol toescape from the polyester melt.

[0064] As the polyester melt is fed into successive vessels, themolecular weight and thus the intrinsic viscosity of the polyester meltincreases. The temperature of each vessel is generally increased and thepressure decreased to allow greater polymerization in each successivevessel. The final vessel is generally operated at a pressure of fromabout 0 to 5.5 kPa. Each of the polymerization vessels communicates witha flash vessel. The retention time in the polymerization vessels and thefeed ratio of the reactants into the continuous process are determinedin part based on the target molecular weight of the poly st r.

[0065] The polymerization catalyst employed in the continuous process isgenerally added prior to, at the start of, or during the polymerizationstage.

[0066] When the polymerization process is completed, the resultingpolyester, which is still in the form of a melt, is generally filteredand the typically extruded and pelletized before being worked up intospecific polyester articles or injection molded in a preform or coatinginto an item such as a bottle. Such steps are also typically labeled as“polyester processing” but refer of course to later working of thefinished polyester rather than to the chemical processing steps used toform the polyester in the first place.

[0067] For example, polyester melt may be extruded into polyestersheets, filaments, pellets, chips or similar particles (so-calledprimary extrusion step). Preferably, the polyester melt is extrudedshortly or immediately after exiting the polycondensation stage,whereupon it is quenched, for example in a water trough or alternativecooling unit. The formation of pellets or chips is particularlyconvenient for storage, transport and handling purposes.

[0068] The pellets of chips may be subjected to solid statepolymerization (SSP), for example, to raise the intrinsic viscosity to0.7 to 1.2 dl/g, preferably to about 0.83 dl/g.

[0069] In order to produce the final polyester articles, in the form ofbottles, filaments, sheets, molded articles and the like, the pellets orchips are re-melted and re-extruded or injection molded. The extrusionand injection molding conditions are conventional. For example, thepolyester may be extruded at a temperature in the range of 240 to 315°C.

[0070] A preferred polyhydric alcohol of the formula I is, for examplestarch, cellulose, a sugar or a sugar alcohol, especially cellulose orstarch.

[0071] An especially preferred polyhydric alcohol of the formula I ispoly(ethylene-co-vinyl alcohol), poly(styrene-co-allyl alcohol),sorbitol, isomalt, xylitol, sucrose, mucic acid dibutylester, mucic aciddi(phenyl-1-ethyl)ester, pentaerythritol, maltose, maltitol,maltopentaose hydrate, maltoheptaose, maltot traose, maltulosemonohydrate, D,L-glucose, dextrose, D-mannitol, trimethylol propane,triethylol propane or glycerol.

[0072] Preferred compounds of the formula II are those in which

[0073] R₁ is hydrogen, C₁-C₁₂alkyl, phenyl, biphenyl, naphthyl,—CH₂—O—C₁-C₁₂alkyl or —CH₂—S—C₁-C₁₂alkyl, and

[0074] R₂ is C₁-C₁₂alkyl, phenyl, biphenyl, naphthyl, —CH₂—O—C₁-C₁₂alkylor —CH₂—S—C₁-C₁₂alkyl.

[0075] Of special interest are compounds of the formula II wherein R₁and R₂ are C₄-C₁₂alkyl.

[0076] The preferred radicals R′₁ and R′₂ are identical to the preferredradicals R₁ and R₂.

[0077] An especially preferred component (c) is for example a compoundof the formula H1, H2, H3, H4, H5, H6, H7, H8, H9, H10, H11, H12, H13,H14or H15

[0078] in which

[0079] m is a number from the range from 2 to 200,

[0080] Preferred hydroxylamines of component (e) are compounds of thformula IX

[0081] wherein

[0082] T₁ is straight or branched chain alkyl of 1 to 36 carbon atoms,cycloalkyl of 5 to 12 carbon atoms, aralkyl of 7 to 9 carbon atoms, orsaid aralkyl substituted by one or two alkyl of 1 to 12 carbon atoms orby one or two halogen atoms; and

[0083] T₂ is hydrogen, or independently has the same meaning as T₁.

[0084] In the present invention the compounds of component (e) are, forexample, N,N-dihydrocarbylhydroxylamines of the formula IX wherein T₁and T₂ are independently benzyl, methyl, ethyl, octyl, lauryl, dodecyl,tetradecyl, hexadecyl, heptadecyl or octadecyl, or wherein T₁ and T₂ areeach the alkyl mixture found in hydrogenated tallow amine.

[0085] The compounds of component (e) in the present compositions andmethods are, e.g. N,N-dihydrocarbylhydroxylamines selected from thegroup consisting of N,N-dibenzylhydroxylamine, N,N-diethylhydroxylamine,N,N-dioctylhydroxylamine, N,N-dilaurylhydroxylamine,N,N-didodecylhydroxylamine, N,N-ditetradecylhydroxylamine,N,N-dihexadecylhydroxylamine, N,N-dioctadecylhydroxylamine,N-hexadecyl-N-tetradecylhydroxylamine,N-hexadecyl-N-heptadecylhydroxylamine,N-hexadecyl-N-octadecylhydroxylamine,N-heptadecyl-N-octadecylhydroxylamine, N-methyl-N-octadecylhydroxylamineand N,N-di(hydrogenated tallow)hydroxylamine.

[0086] Component (e) in the present invention may be for example theN,N-di(alkyl)hydroxylamine produced by the direct oxidation ofN,N-di(hydrogenated tallow)amine [Irgastab FS-042 (RTM), Ciba SpecialtyChemicals Corp.].

[0087] The hydroxylamines are for example those disclosed in U.S. Pat.No. 4,590,231 or U.S. Pat. No. 4,612,393.

[0088] Preferred nitrones of component (e) are compounds of the formulaX

[0089] wherein

[0090] L₁ is straight or branched chain alkyl of 1 to 36 carbon atoms,cycloalkyl of 5 to 12 carbon atoms, aralkyl of 7 to 9 carbon atoms, orsaid aralkyl substituted by one or two alkyl of 1 to 12 carbon atoms orby one or two halogen atoms; and

[0091] L₂ and L₃ are independently hydrogen, straight or branched chainalkyl of 1 to 36 carbon atoms, cycloalkyl of 5 to 12 carbon atoms,aralkyl of 7 to 9 carbon atoms, or said aralkyl substituted by one ortwo alkyl of 1 to 12 carbon atoms or by one or two halogen atoms; or L₁and L₂ together form a five- or six-membered ring including the nitrogenatom.

[0092] The nitrones of component (e) may be the corresponding oxidationproducts of the hydroxylamines. That is to say, the nitrones ofcomponent (e) may be nitrone analogues of the hydroxylamines. Thenitrones may be for example, N-benzyl-α-phenylnitrone,N-ethyl-α-methylnitrone, N-octyl-α-heptylnitrone,N-lauryl-α-undecylnitrone, N-tetradecyl-α-tridcylnitrone,N-hexadecyl-α-pentadecylnitrone, N-octadecyl-α-heptadecylnitrone,N-hexadecyl-α-heptadecylnitrone, N-ocatadecyl-α-pentadecylnitrone,N-heptadecyl-α-heptadecylnitrone, N-octadecyl-α-hexadecylnitrone,N-methyl-α-heptadecylnitrone the nitrone derived fromN,N-di(hydrogenated tallow)hydroxylamine or the compound of the formulaN1

[0093] The nitrones of component (e) may be for example as described inU.S. Pat. No. 4,898,901.

[0094] Of special interest is a process for the preparation of astabilized polyester that is low in the generation of aid hydes whereinthe diacid is terephthalic acid or isophthalic acid; the diester is aC₁-C₄alkyl ester of terephthalic acid or isophthalic acid; the diol isethylene glycol; component (a) is poly(ethylene-co-vinyl alcohol),poly(styrene-co-allyl alcohol), maltitol, isomalt, sorbitol, xylitol,sucrose, mucic acid dibutylester, mucic acid di(phenyl-1-ethyl)ester,pentaerythritol or dipentaerythritol; component (b) isdi-iso-octyl-phosphinic acid; component (c) is a compound of the formulaH1, H2, H3, H4, H5, H 6, H7, H8, H9, H10, H11, H12, H13, H14 or H15according to claim 13; component (d) is polyacrylanilide, an anionicacrylic polymer or a cationic acrylamide copolymer; and component (e) isN,N-dioctadecylhydroxylamine or a compound of the formula N1

[0095] A preferred embodiment of the present invention is the use of astabilizer selected from the group consisting of components (a), (b),(c), (d) or (e) for the preparation of polyesters that are low in thegeneration of aldehydes during melt processing of the polyesters.

[0096] Likewise, the instant invention pertains to a polyesterobtainable by the process of the instant invention; and to mineral waterbottles, films, trays, containers, baby toys and automobile wind shieldsprepared from a polyester obtained by the process of the instantinvention.

[0097] The instant invention also pertains to a process for forming abottle preform or a PET bottle or container suitable for storing water(mineral, natural, ozonated) or other foodstuffs, which allows thedesirable taste of the water or foodstuff after packaging to remainunaltered after being placed in said bottle or container prepared fromthe polyester of the instant invention.

[0098] The following examples are for illustrative purposes only and arenot to be construed to limit the scope of the instant invention in anymanner whatsoever.

[0099] Analytical Procedures:

[0100] Intrinsic Viscosity (I.V.): 1 g of polymer is dissolved in 100 gof a 1:1 mixture of phenol and dichlorobenzene. The viscosity of thissolution is measured at 30° C. in an Ubelode-Viscosimeter andrecalculated to the instrinsic viscosity.

[0101] Acetaldehyde Analysis: The concentration of acetaldehyde in PETis quantitatively determined using a thermal desorption GC-MS methodadapted from B. Nijassen et al., Packaging Technology and Science, 9,175 (1996); S. Yong Lee, SPE ANTEC 1997, pp 857-861; and M. Dong et al.,J. Chromatographic Science, 18, 242 (1980). A general example followsbelow:

[0102] The PET samples are analyzed, in duplicate, by weighing 250 mg ofpowdered PET pellets (cryogenically pulverized) in a 5 ml crimp sealedheadspace vial. The sample vial is heated at 120° C. for one hour in aTekmar model 5000 static headspace analyzer. The headspace gas (5 cc) isthen transferred via a heated transfer line to a Fisons MD-800 GC-MSsystem for SIR detection of the acetaldehyde. The acetaldehyde isdetected by monitoring its fragment ions of 29 and 44 m/e. The Total IonCurrent (TIC) of the GC-MS is also monitored in the retention timeregion of 4-8 minutes. The presence of acetaldehyde in the samples isconfirmed by three different detectors. By using a known acetaldehydevalue for PET, the ration of peak areas for the known PET resin and forthe experimental PET resins are compared and the amount of acetaldehydein the experimental PET can be obtained. Alternatively a commerciallyavailable standard of acetaldehyde in water (approx. 1 ppm) may be usedto establish calibration of the GC-MS.

EXAMPLE 1 Preparation of Polyethylene Terephthalate

[0103] 1621.3 g of ethylene glycol, 3338.5 g of terephthalic acid, 66.8g of isophthalic acid, 1.36 g of antimony trioxide are mixed within ametal container with a stabilizer in an amount as indicated in Table 1.The mixture is transferred into a 10 liter reactor (stainless steel)fitted with stirrer, refluxing unit and an outlet-die at the bottom ofthe reactor. The reactor is pressurized with nitrogen up to 6 bars. Themonomer mixture is heated from room temperature to 250° C. within 30minutes. A water/ethylene glycol mixture is distilled off for 3.5 hours.The temperature is increased consecutively to 280° C. Within the next 5hours the pressure is continuously reduced to further distill off waterand ethylene glycol. Then polyester product is extruded through thebottom die, cooled to room temperature in a water bath and pelletized toyield clear polyethylene terephthalate (PET) granules. From thesegranules the acetaldehyde content in ppm [Total Ion Current method(TIC)] and the Intrinsic Viscosity (I.V.) in dl/g was measured. Theresults are summarized in Table 1. TABLE 1 Acetaldehyde Acetalde-content in ppm hyde content Exam- Stabilizer after polycon- I.V. in ppmafter ple [weight %] densation [dl/g] extrusion 1a^(a)) none 170  0.755.0 1b^(b)) 0.20% compound 101^(c)) 40 0.50 1.6 1c^(b)) 0.09% compound101^(c)) 76 0.68 1d^(b)) 0.05% compound 101^(c)) 62 0.65 2.8 1e^(b))0.10% compound 102^(d)) 72 0.73 1f^(b)) 0.10% compound 103^(e)) 49 0.701g^(b)) 0.10% compound 104^(f)) 58 0.57 1h^(b)) 0.10% compound 105^(g))82 0.70 1i^(b)) 0.10% compound 106^(h)) 94 0.68 1j^(b)) 0.10% compound107^(i)) 78 0.64 1k^(b)) 0.10% compound 108^(j)) 62 0.72 1l^(b)) 0.10%compound 109^(k)) 78 0.64 3.9 1m^(b)) 0.10% compound 110^(l)) 97 0.690.25% compound 111^(m)) 1n^(b)) 0.10% compound 112^(n)) 99 0.70 1o^(b))0.05% compound 113^(o)) 58 0.68 2.3 1p^(b)) 0.05% compound 114^(p)) 570.69 1q^(b)) 0.10% compound 115^(q)) 52 0.71 3.8 1r^(b)) 0.10% compound116^(r)) 56 0.30 1s^(b)) 0.05% compound 117^(s)) 53 0.67 1t^(b)) 0.05%compound 118^(t)) 78 0.70 1u^(b)) 0.10% compound 119^(u)) 41 0.591v^(b)) 0.10% compound 120^(v)) 29 0.48 1w^(b)) 0.10% compound 121^(w))46 0.62 1x^(b)) 0.10% compound 122^(x)) 37 0.65 1y^(b)) 0.10% compound123^(y)) 54 0.62 1z^(b)) 0.10% compound 124^(z)) 71 0.65 1aa^(b)) 0.10%compound 125^(aa)) 34 0.52 1ab^(b)) 0.10% compound 126^(ab)) 72 0.691ac^(b)) 0.10% compound 127^(ac)) 52 0.58 1ad^(b)) 0.10% compound128^(ad)) 36 0.61 1ae^(b)) 0.10% compound 129^(ae)) 77 0.71 1af^(b))0.05% compound 130^(af)) 68 0.73

[0104]

[0105] n) Compound 112 is di-iso-octyl-phosphinic acid.

[0106] o) Compound 113 is Tinuvin 123 (RTM) (Ciba Specialty ChemicalsInc.) of the formula H1

[0107] p) Compound 114 is Tinuvin 622 (RTM) (Ciba Specialty ChemicalsInc.) of the formula H2

[0108]  in which m is a number from the range from 2 to 200.

[0109] q) Compound 115 is polyacrylanilide with a number averagemolecular weight Mn: 10600 g/mol; weight average molecular weight Mw:45000 g/mol measured by GPC, eluent and solvent is tetrahydrofurane;internal standard is cyclohexane.

[0110] r) Compound 116 is dipentaerythritol.

[0111] s) Compound 117 is Tinuvin 765 (RTM) (Ciba Specialty ChemicalsInc.) of the formula H4

[0112] t) Compound 118 is Tinuvin 770 (RTM) (Ciba Specialty ChemicalsInc.) of the formula H8

[0113] u) Compound 119 is a compound of the formula H9

[0114] v) Compound 120 is a compound of the formula H10

[0115] w) Compound 121 is a compound of the formula H11

[0116] x) Compound 122 is a compound of the formula H12

[0117] y) Compound 122 is a compound of the formula H13

[0118] z) Compound 124 is a compound of the formula H14

[0119] aa) Compound 125 is a compound of the formula H15

[0120] ab) Compound 126 is Magnafloc 611 (RTM) (Ciba Specialty ChemicalsInc.), an anionic acrylic polymer, sold as flocculant.

[0121] ac) Compound 127 is Zetag 7633 (RTM) (Ciba Specialty ChemicalsInc.), a cationic acrylamide copolymer, sold as sewage and industrialsludge flocculant.

[0122] ad) Compound 128 is Magnafloc 139 (RTM) (Ciba Specialty ChemicalsInc.), a weak anionic acrylic polymer with low molecular weight, sold asflocculant.

[0123] ae) Compound 129 is a compound of the formula N1 (nitrone)

[0124] af) Compound 130 is N,N-dioctadecylhydroxylamine.

[0125] The polycondensation in the melt as described above is followedby a solid state polycondensation (SSP) for further increasing themolecular weight by monitoring the instrinsic viscosity. Furthermore,this process decreases the content of acetaldehyde.

[0126] The following description illustrates the general technicalprocedure: 2.5 kg of polyethylene terephthalate according to Examples lais placed at room temperature into a vacuum tumbling dryer. Duringcontinuous tumbling of the polyethylene terephthalate under a vacuum of0.06 mbar the following temperature protocol is followed: a) 1 hour at120° C., b) 1 hour at 160° C., c) 1 hour at 190° C., and d) 5 hours at220° C. The obtained product revealed an intrinsic viscosity value of0.82 dl/g and a content of acetaldehyde of 0.85 ppm. Additionally allpolyethylene terephthalate samples according to Examples 1b-1q weretreated similar under solid state polycondensation condition. The targetintrinsic viscosity value of 0.80±0.02 is achieved by adjusting thesolid state polycondensation processing conditions like for example timeand temperature. The content of acetaldehyde after solid statepolycondensation of Examples 1b-1q is proven to be below 1 ppm in allsamples.

[0127] Examples 1a, 1b, 1d, 1l, 1o and 1q which were treated under solidstate polycondensation condition were additionally melt extruded in aLeistritz 18 mm co-rotating, intermeshing twin screw extruder at atemperature range of 280-284° C. From these extruded polyethyleneterephthalate samples the content of acetaldehyde is measured. Theresults which are summarized in the last column of Table 1 clearlyreveal that a significant reduction of the rebuilding of acetaldehydeduring extrusion is observed in Examples 1b, 1d, 1l, 1o and 1q accordingto the invention which contain a stabilizer in comparison to Example 1awhich does not contain a stabilizer.

What is claimed is:
 1. A process for the preparation of a stabilizedpolyester that is low in the generation of aldehydes which comprisesreacting one or more diacids with one or more diols in an esterificationprocess, and/or one or more diesters with one or more diols in atransesterification process in the presence of an effective amount of astabilizer selected from the group consisting of a) a polyhydric alcoholof the formula I E—(OH)_(n)  (I)  wherein n is 3 to 4000, and  E is analiphatic, cycloaliphatic, aromatic or a mono-, di- or poly-sucrosemoiety; with the proviso that, if n is 3 or 4 and E is an aliphaticmoiety, then additionally at least one sterically hinderedhydroxyphenylalkylphosphonic ester or monoester is present; b) acompound of the formula II

 wherein  R₁ is hydrogen, C₁-C₂₀alkyl, phenyl or C₁-C₄alkyl substitutedphenyl; biphenyl, naphthyl, —CH₂—O—C₁-C₂₀alkyl or —CH₂—S—C₁-C₂₀alkyl, R₂ is C₁-C₂₀alkyl, phenyl or C₁-C₄alkyl substituted phenyl; biphenyl,naphthyl, —CH₂—O—C₁-C₂₀alkyl or —CH₂—S—C₁-C₂₀alkyl, or R₁ and R₂together are a radical of the formula III

 wherein  R₃, R₄ and R₅ independently of each other are C₁-C₂₀alkyl,phenyl or C₁-C₄alkyl substituted phenyl, c) a sterically hindered aminewhich comprises at least a radical of the formula IV or V

 wherein  G is hydrogen or methyl, and  G₁ and G₂ are hydrogen, methylor together are oxygen, d) a polyacrylamide of the formula VI

 wherein  R′₁ and R′₂ are independently of each other hydrogen,C₁-C₂₀alkyl, phenyl or C₁-C₄-alkyl substituted phenyl; biphenyl,naphthyl, —CH₂—O—C₁-C₂₀alkyl or —CH₂—S—C₁-C₂₀alkyl; or R′₁ and R′₂together are a radical of the formula III

 R′₁ and R′₂ together with the nitrogen atom to which they are attachedform an unsubstituted or C₁-C₄alkyl substituted imidazolyl, pyrrolyl,pyrrolidonyl, piperidinyl or piperazinyl ring; and  q is 5 to 300000; or a polyacrylamide copolymer wherein the comonomer is an acrylic acid, anacrylic acid salt or an acrylic ester; or e) hydroxylamines and/ornitrones.
 2. A process according to claim 1, comprising components (a),(b), (c) or (d) with the proviso that the comonomer in component (d) isacrylic acid or an acrylic ester.
 3. A process according to claim 1,comprising in addition to components (a), (b), (c), (d) or (e) at leastone sterically hindered hydroxyphenylalkylphosphonic ester or monoester.4. A process according to claim 3, wherein the sterically hinderedhydroxyphenylalkylphosphonic ester or monoester is a compound of theformula VII

wherein R₆ is isopropyl, tert-butyl, cyclohexyl or cyclohexyl which issubstituted by 1-3 C₁-C₄alkyl groups, R₇ is hydrogen, C₁-C₄alkyl,cyclohexyl or cyclohexyl which is substituted by 1-3 C₁-C₄alkyl groups,R₈ is C₁-C₂₀alkyl, unsubstituted or C₁-C₄alkyl-substituted phenyl ornaphthyl, R₉ is hydrogen, C₁-C₂₀alkyl, unsubstituted orC₁-C₄alkyl-substituted phenyl or naphthyl; or is $\frac{M^{r +}}{r};$

M^(r+) is an r-valent metal cation, p is 1, 2, 3, 4, 5 or 6, and r is 1,2 or
 3. 5. A process according to claim 3, wherein the stericallyhindered hydroxyphenylalkylphosphonic ester or mono ster is a compoundof the formula P1 or P2


6. A process according to claim 1, wherein the diacid is selected fromthe group consisting of aromatic dicarboxylic acids having 8 to 14carbon atoms, aliphatic dicarboxylic acids having 4 to 12 carbon atoms,cycloaliphatic dicarboxylic acids having 8 to 12 carbon atoms, andmixtures thereof.
 7. A process according to claim 1, wherein the diacidis terephthalic acid, isophthalic acid, o-phthalic acid, naphthalenedicarboxylic acid, cyclohexane dicarboxylic acid, cyclohexanediaceticacid, diphenyl-4,4′-dicarboxylic acid, succinic acid, glutaric acid,adipic acid, sebacic acid and mixtures thereof.
 8. A process accordingto claim 1 wherein the diacid is terephthalic acid or 2,6-naphthalenedicarboxylic acid.
 9. A process according to claim 1 wherein the diol isa compound of the formula VIII HO—R—OH  (VIII) wherein R is analiphatic, cycloaliphatic or aromatic moiety of 2 to 18 carbon atoms.10. A composition according to claim 1 wherein the diol is ethyleneglycol, diethylene glycol, triethylene glycol, propane-1,3-diol,butane-1,4-diol, pentane-1,5-diol, hexane-1,6-diol,1,4-cyclohexanedimethanol, 3-methylpentane-2,4-diol,2-methylpentane-1,4-diol, 2,2-diethylpropane-1,3-diol,1,4-di-(hydroxyethoxy)benzene, 2,2-bis(4-hydroxycyclohexyl)-propane,2,4-dihydroxy-1,1,3,3-tetramethylcyclobutane,2,2-bis-(3-hydroxyethoxyphenyl)propane,2,2-bis-(4-hydroxypropoxyphenyl)ethane and mixtures thereof.
 11. Aprocess according to claim 1 wherein component (a) ispoly(ethylene-co-vinyl alcohol), poly(styrene-co-allyl alcohol),sorbitol, isomalt, xylitol, sucrose, mucic acid dibutylester, mucic aciddi(phenyl-1-ethyl)ester, pentaerythritol, maltose, maltitol,maltopentaose hydrate, maltoheptaose, maltotetraose, maltulosemonohydrate, D,L-glucose, dextrose, D-mannitol, trimethylol propane,triethylol propane or glycerol.
 12. A process according to claim 1wherein R₁ and R₂ are C₄-C₁₂alkyl.
 13. A process according to claim 1wherein component (c) is a compound of the formula H1, H2, H3, H4, H5,H6, H7, H8, H9, H10, H11, H12, H13, H14or H15

in which m is a number from the range from 2 to 200,


14. A process according to claim 1, wherein hydroxylamines of component(e) ar compounds of the formula IX

wherein T₁ is straight or branched chain alkyl of 1 to 36 carbon atoms,cycloalkyl of 5 to 12 carbon atoms, aralkyl of 7 to 9 carbon atoms, orsaid aralkyl substituted by one or two alkyl of 1 to 12 carbon atoms orby one or two halogen atoms; and T₂ is hydrogen, or independently hasthe same meaning as T₁.
 15. A process according to claim 14, whereinhydroxylamines of component (e) are dioctadecylhydroxylamine orN,N-di(alkyl)hydroxylamine produced by the direct oxidation ofN,N-di(hydrogenated tallow)amine.
 16. A process according to claim 1,wherein nitrones of component (e) are compounds of the formula X

wherein L₁ is straight or branched chain alkyl of 1 to 36 carbon atoms,cycloalkyl of 5 to 12 carbon atoms, aralkyl of 7 to 9 carbon atoms, orsaid aralkyl substituted by one or two alkyl of 1 to 12 carbon atoms orby one or two halogen atoms; and L₂ and L₃ are independently hydrogen,straight or branched chain alkyl of 1 to 36 carbon atoms, cycloalkyl of5 to 12 carbon atoms, aralkyl of 7 to 9 carbon atoms, or said aralkylsubstituted by one or two alkyl of 1 to 12 carbon atoms or by one or twohalogen atoms; or L₁ and L₂ together form a five- or six-membered ringincluding the nitrogen atom.
 17. A process according to claim 1 whereinthe diacid is terephthalic acid or isophthalic acid; the diester is aC₁-C₄alkyl ester of terephthalic acid or isophthalic acid; the diol isethylene glycol; component (a) is poly(ethylene-co-vinyl alcohol),poly(styrene-co-allyl alcohol), maltitol, isomalt, sorbitol, xylitol,sucrose, mucic acid dibutylester, mucic acid di(phenyl-1-ethyl)ester,pentaerythritol or dipentaerythritol; component (b) isdi-iso-octyl-phosphinic acid; component (c) is a compound of the formulaH1, H2, H3, H4, H5, H6, H7, H8, H9, H10, H11, H12, H13, H14 or H15according to claim 13; component (d) is polyacrylanilide, an anionicacrylic polymer or a cationic acrylamide copolymer; and component (e) isdioctadecylhydroxylamine or a compound of the formula N1


18. A polyester obtainable by a process according to claim
 1. 19. Use ofa stabilizer selected from the group consisting of components (a), (b),(c), (d) or (e) according to claim 1 for the preparation of polyestersthat are low in the generation of aldehydes during melt processing ofthe polyesters.
 20. Mineral water bottles, films, trays, containers,baby toys and automobile wind shields prepared from a polyester asprepared in claim 1.